Editing Selective reduction (section)

==Medical use==
[[File:Acardiac twin.jpg|thumb|[[Twin reversed arterial perfusion|TRAP syndrome]]. On the left, an acardiac twin which lacks both a heart and head. On the right, the "pump twin" which supplies the acardiac twin with blood. A selective termination of the acardiac twin reduces the risk of death of the pump twin. ]]
Selective reduction is used when a mother is carrying an unsafe or undesirable number of fetuses in a [[multiple pregnancy]], which are common in [[assisted reproductive technology|medically assisted pregnancies]]. The result is a reduction in the number of fetuses to a number that is more safe for the mother and the remaining fetuses or more compatible with socio-economic constraints on the caregivers.<ref name="ACOG2017" /><ref name="Zipori2017">{{cite journal |last1=Zipori |first1=Y |last2=Haas |first2=J |last3=Berger |first3=H |last4=Barzilay |first4=E |title=Multifetal pregnancy reduction of triplets to twins compared with non-reduced triplets: a meta-analysis. |journal=Reproductive Biomedicine Online |date=September 2017 |volume=35 |issue=3 |pages=296–304 |doi=10.1016/j.rbmo.2017.05.012 |pmid=28625760}} {{open access}}</ref><ref name="Evans2014" /> It is also used in cases of multiple pregnancy where at least one of the fetuses is [[ectopic pregnancy|implanted outside the uterus]] to preserve the life of the mother and the fetus in the uterus,<ref>{{cite journal |last1=Yeh |first1=J |last2=Aziz |first2=N |last3=Chueh |first3=J |title=Nonsurgical management of heterotopic abdominal pregnancy. |journal=Obstetrics and Gynecology |date=February 2013 |volume=121 |issue=2 Pt 2 Suppl 1 |pages=489–95 |doi=10.1097/AOG.0b013e3182736b09 |pmid=23344419|s2cid=40913509 |url=https://journals.lww.com/greenjournal/Abstract/2013/02001/Nonsurgical_Management_of_Heterotopic_Abdominal.26.aspx |url-access=subscription }}</ref> and when one or more of the fetuses has a serious and incurable disease.<ref name="Legendre2013" /> One example of is [[Twin reversed arterial perfusion|TRAP]] syndrome, where one fetus lacks a heart; the second twin, termed a "pump" twin therefore supplies the second twin with blood, leading to heart failure and death in the second twin in 50-75% of cases if the acardiac twin is not terminated.<ref>{{Cite journal |last1=Beriwal |first1=Sridevi |last2=Impey |first2=Lawrence |last3=Ioannou |first3=Christos |date=Oct 2020 |title=Multifetal pregnancy reduction and selective termination |journal=The Obstetrician & Gynaecologist |language=en |volume=22 |issue=4 |pages=284–292 |doi=10.1111/tog.12690 |issn=1467-2561|doi-access=free }}</ref>

While the data is weak, due to the small sizes of studies and the lack of randomized controlled trials, as of 2017 it appeared that when short term perinatal outcomes in multiple pregnancies reduced to twins are compared to those of non-reduced triplets, there were fewer deaths among the babies born to mothers who underwent reduction, the twins were born later and were less likely to be [[Preterm birth|premature]], and had higher birthweight.<ref name=Zipori2017/> As of 2017, longterm outcomes were not well understood.<ref name=Zipori2017/> A 2015 Cochrane review found no randomized clinical trials to evaluate.<ref name=Cochrane2015>{{cite journal|last1=Dodd|first1=JM|last2=Dowswell|first2=T|last3=Crowther|first3=CA|title=Reduction of the number of fetuses for women with a multiple pregnancy.|journal=The Cochrane Database of Systematic Reviews|date=4 November 2015|volume=11|issue=11|pages=CD003932|pmid=26544079|doi=10.1002/14651858.CD003932.pub3|pmc=7104508|s2cid=38648757}} {{open access}}</ref>

===Outcomes===
Generally selective reduction reduces the risk of preterm birth, leading to better outcomes for both mothers and the newborns.<ref name=Obican2015>{{cite journal |last1=Običan |first1=S |last2=Brock |first2=C |last3=Berkowitz |first3=R |last4=Wapner |first4=RJ |title=Multifetal Pregnancy Reduction. |journal=Clinical Obstetrics and Gynecology |date=September 2015 |volume=58 |issue=3 |pages=574–84 |doi=10.1097/GRF.0000000000000119 |pmid=26083128|s2cid=10307261 }}</ref>

It appears that reduction of triplets, where each triplet is in its own placenta, to twins results in a lower risk of preterm birth and does not increase the risk of miscarriage. In triplets where two of the fetuses share a placenta and each has its own amniotic sac, it appears, with less certainty, that there is also a lower risk of preterm birth and no increase in the risk of miscarriage.<ref name=":0">{{cite journal |last1=Anthoulakis |first1=C |last2=Dagklis |first2=T |last3=Mamopoulos |first3=A |last4=Athanasiadis |first4=A |title=Risks of miscarriage or preterm delivery in trichorionic and dichorionic triplet pregnancies with embryo reduction versus expectant management: a systematic review and meta-analysis. |journal=Human Reproduction (Oxford, England) |date=1 June 2017 |volume=32 |issue=6 |pages=1351–1359 |doi=10.1093/humrep/dex084 |pmid=28444191|s2cid=3778609 |doi-access=free }}</ref>